1. Field of the Invention
This invention relates to a method and apparatus for controlling and monitoring pressure pot shot peening machines. Such structures of this type, generally, allow the user to determine and control the force of the shot as it leaves the shot peening nozzle.
2. Description of the Related Art
The use of shot peening is relatively well known. In particular, a stream of shot (i.e., particles) is directed at the surface at a high velocity. The shot is directed at a workpiece so as to cause plastic deformation of the surface of the workpiece, often a metal surface. The shot peening is often used to increase fatigue strength, although the process may be applied for other purposes.
Various shot peening devices and techniques have been developed over the years. Shot peening systems, generally, have (or can be readily equipped with) mass flow controllers. Such controllers are used to control the flow of shot to the shot peening gun. One common type of mass flow controller for use with shot made from magnetic material has an electromagnet which is pulsed in order to allow passage of a metered amount of shot into a shot peening gun. This common type of mass flow controller uses internal feedback to stabilize the mass flow rate (i.e., the amount of shot metered in a given time). A control may be used to set the mass flow rate to a desired value. A display may be used to indicate the flow rate.
Although the mass flow rate is useful information, it is insufficient by itself to give an indicate of the quality of the shot peening applied to a particular surface.
Although some measurement techniques have been used in conjunction with the shot peening process, such prior techniques have been inadequate to conveniently and inexpensively provide an indication of the quality of a shot peening technique. The general absence of simple and inexpensive techniques to measure the quality of shot peening inhibits one's confidence that consistent shot peening results may be obtained. A further problem of some shot peening systems has been their inability to halt the shot peening when a nozzle is partly cogged, an air leak occurs, or some other malfunction happens.
Finally, it is known in shot peening control and monitoring systems to measure the reaction force at the nozzle by a force sensor. Exemplary of such prior art shot peening systems achieving a modicum of success in this regard is U.S. Pat. No. 4,805,429 to R. A. Thompson, which is assigned to the same assignee as the present invention. The Thompson patent discloses the importance of knowing the shot velocity in a shot peening operation. The Thompson patent further describes a way to measure shot velocity as the force required to accelerate shot from the gun divided by the mass flow rate of shot. The shot mass flow rate is measured by a commercial sensor and the reaction force by a commercial force sensor mounted at the base of the gun. A load cell mounted on the gun has several advantages, but in certain applications it also has some drawbacks. For example, in the case of a robot gun positioner's weight and acceleration affects must be reconciled as must the space needed for the sensing element. Therefore, an advantageous system would be presented if the reaction force were determined in an easier manner.
It is apparent from the above that there exists a need in the art for an apparatus and method for controlling and monitoring pressure pot shot peening machines which is capable of determining the reaction force at the nozzle, and which at least equals the pressure determination characteristics of the known systems, particularly those of the highly advantageous type disclosed in the above-referenced Thompson patent, but which at the same time determines the pressure in an easier manner. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.